OpenMP: C/C++ parse 'omp allocate'

OpenMP: C/C++ parse 'omp allocate'

gcc/c-family/ChangeLog:

	* c-pragma.c (omp_pragmas): Add 'allocate'.
	* c-pragma.h (enum pragma_kind): Add PRAGMA_OMP_ALLOCATE.

gcc/c/ChangeLog:

	* c-parser.c (c_parser_omp_allocate): New.
	(c_parser_omp_construct): Call it.

gcc/cp/ChangeLog:

	* parser.c (cp_parser_omp_allocate): New.
	(cp_parser_omp_construct, cp_parser_pragma): Call it.

gcc/testsuite/ChangeLog:

	* c-c++-common/gomp/allocate-5.c: New test.